The invention relates to a vessel for the generation of synthesis gas at a high pressure (thirty bar or more), using hydrocarbons, particularly natural gas, naphtha and/or refinery gas in a catalytic endothermic reforming section with a cylindrical pressure vessel and a plurality of reformer tubes heated externally and filled with a catalyst, and a mixture of hydrocarbons and water vapor entering the reformer tubes which are positioned by means of a common plate. The reforming gas generated in said tubes flows from the tubed section into a partial oxidation section in which hydrocarbons and oxygen or oxygen-rich gas are admixed. The oxidation section has the shape of a pressure vessel closed at one end, with the reformer tubes penetrating into said section.
The synthesis gas which mainly contains hydrogen and carbon monoxides is the raw material for a number of commercial-scale synthesis plants such as methanol or ammonia plants. It is also possible to produce pure hydrogen, provided the synthesis gas is subjected to an appropriate treatment.
Vessels for synthesis gas generation are known, in which the following process steps are used:
catalytic endothermic steam reforming (I) and PA1 partial autothermic oxidation (II) PA1 m.sub.o is the mass of the steam from an opening in the plane of the reformer tube outlets. PA1 m.sub.1 is the mass of the gas stream produced with the aid of m.sub.o. PA1 .rho..sub.1 and .rho..sub.o are the densities of the steams involved. PA1 d is the diameter of the opening in the plane of the reformer tube outlets.
and in which the reformer tubes filled with a catalyst are heated with hot reaction gas generated in partial oxidation step II.
West German Pat. No. 32 44 252, for example, describes a vessel in which a first stream of hydrocarbons is mixed with steam and subjected to the steam reforming reaction in the reformer tubes filled with a catalyst. The process gas generated in this reaction step leaves the reformer tubes suspended perpendicularly in a cylindrical brick-lined vessel and then enters an untubed chamber under the reformer tube ends which is referred to as the mixing chamber. The temperature of the gas leaving reaction step I is normally over 700.degree. C. The second stream of hydrocarbons, which need not have the parameters of the first stream (quantity, etc.), is fed to said chamber, thereby admixing oxygen or oxygen-rich gas. The gases react with each other (reaction step II). The gases in the immediate vicinity of the above mentioned reactants also take part in the step II reaction.
The temperature of the gas generated in reaction step II is approximately 1400.degree. to 2100.degree. C. and, consequently, it exceeds considerably the temperature of the gas generated in reaction step I. The gas streams from reaction steps I and II should be thoroughly mixed in the mixing chamber until the mixture has a uniform temperature. The equilibrium reactions taking place simultaneously are called reaction step III, the temperature being in excess of 950.degree. C., preferably 1100.degree. C., and governing the synthesis gas composition. This gas flows in a counter-current to the gases generated in reaction step I and enters the tubed part of the catalytic reforming section, the tubes of which are heated to the temperature required for reaction step I.
The gas generated in reaction step I has a high residual methane content while the gas stream from step II contains only traces of methane. The gas stream from reaction step III has a target methane content which is compatible with the reaction temperature, for example less than 1%, preferably less than 0.5%. However, this reaction temperature and the gas composition which can be calculated on this basis can only be achieved if the gas streams from reaction steps I and II are completely mixed, i.e. leaving no gas striae. In order to ensure an optimum performance, it is imperative that the gases be completely mixed prior to entering the cooling section (tubed reforming section). The device described in patent No. 32 44 252 does not ensure an appropriate mixing of the gas streams.
Another vessel is known from U.S. Reissue Pat. No. 24,311, in which the hydrocarbons are mixed with steam and then subjected to a limited catalytic endothermic steam reforming process which takes place in a cylindrical pressure vessel equipped with reformer tubes partly filled with a catalyst. Oxygen-carrying tubes are installed in the center of the reformer tubes. At the outlet of said tubes, the partly reformed hydrocarbons are mixed with heated oxygen and subjected to a simultaneous partial autothermic oxidation. The lower part of the cylindrical pressure vessel is an untubed reaction chamber in which the reaction gases return at the chamber bottom in order to flow upwards and to heat the reformer tubes. From the technological and metallurgical point of view, it is very difficult to mount the oxygen-carrying tubes in the center of the hot reformer tubes and, as a result, this device has never been constructed. Moreover, the design does not permit universal application for various raw materials and is not suitable for the treatment of hydrocarbons in two reaction steps.